1. Field of the Invention
The present invention relates to a method and apparatus for optically communicating data between a stationary member and a rotating member and, more specifically, to a method and apparatus for optically communicating data between a stationary frame and a rotating ring of an X-ray computer tomography apparatus.
2. Description of the Related Art
Various non-contact techniques have been developed to facilitate the optical transmission of data between a rotating member and a stationary member. Some of these techniques have been applied to X-ray computer tomography apparatuses to provide an optical data link for communicating optical data between a rotating ring and a stationary outside frame of the apparatus.
For example, Keller U.S. Pat. No. 4,996,435 discloses an optical system for transmitting data between a stationary member and a rotating member, such as for transmitting data from the rotating ring in a computer tomography apparatus and the stationary frame of the apparatus. In one embodiment, Keller discloses a frame having a plurality of light transmitters symmetrically mounted thereon. The frame is attached to and rotates with the ring of a tomography apparatus. Each of the light transmitters transmits a fan-shaped beam in a fan plane which is within, or parallel to, the plane defined by the frame, such that the beam transmitted by at least one of the light transmitters is incident upon a stationary light receiver at each rotational position of the frame. In another embodiment, Keller discloses that the light transmitters rotate within and in synchronism with the frame such that the light beams transmitted from the light transmitters follow the light receiver as the frame rotates. A drawback of the systems of both embodiments disclosed by Keller is that, because the light beams are transmitted from the light transmitters in a fan shape, the light receiver must have a sufficiently large surface in order to ensure that a sufficient amount of the light is received. Large light receivers, however, tend to be expensive and have poor frequency response characteristics. Further, in the second embodiment disclosed by Keller, the system requires the use of moving parts which are subject to mechanical failure and tend to increase the cost of the system and its size.
Japanese Patent Disclosure (KOKAI) No. 60-108036 ("the 60-108036 publication") discloses an apparatus for optically transmitting data between a rotary system and a stationary system of an X-ray computer tomography apparatus. In a preferred embodiment, the rotary system comprises a rotor having a pair of optical-axis control means which are pivotably and rotatably supported on the rotor, a pair of decelerating means having teeth which are engageable with teeth of the rotor, a pair of disk-shaped cams, and pair of arms supported by the cams. Attached to each arm is a light transmitting device for transmitting light beams from the rotary system. The rotary system is designed such that, as the rotary system rotates, the angle at which the light transmitting devices transmit beams of light varies in proportion to the rotational movement of the rotary system. As a result, the beams transmitted by the transmitting devices are always convergent on a fixed point on the stationary system. A drawback of the system disclosed in the 60-108036 publication, however, is that it requires the use of moving parts to continuously change the angle of transmission of the light beams. Such parts are subject to mechanical failure and tend to increase the cost of the system and its size.